Resin Composition and Display Unit

ABSTRACT

A thin display unit that incorporates a high-luminance, high-contrast display part that is free of image detects caused by the deformation of the display part is provided. The display unit of the present invention includes an image display part  2  and a light-transmitting protective part  3  arranged on the image display part  2 . A cured resin layer  5  is arranged between the display part  2  and the protective part  3 . The cured resin layer  5  has a transmittance of 90% or higher in the visible range and a storage modulus at 25° C. of 1×10 7  Pa or less. The cured resin layer  5  is formed from a resin composition that has a cure shrinkage of 5% or less.

TECHNICAL FIELD

The present invention relates to an image display unit used, forexample, in cellular phones. In particular, the invention relates to animage display unit that includes an image display part and a transparentprotective part arranged on the image display part, with a cured resinarranged between the image display part and the protective part.

BACKGROUND ART

As this type of display unit, a liquid crystal display unit 101 as shownin FIG. 4 is known. The liquid crystal display unit 101 includes aliquid crystal display panel 102 and a transparent protective part 103arranged on the liquid crystal display panel 102. The protective part103 is made of, for example, glass or plastic.

To protect the surface of the liquid crystal display panel 102 and apolarizer (not shown), a spacer 104 is arranged between the liquidcrystal display panel 102 and the protective part 103 to form a gap 105between the liquid crystal display panel 102 and the protective part103.

However, the gap 105 between the liquid crystal display panel 102 andthe protective part 103 scatters light, resulting in decreased contrastand luminance of the display unit. The presence of the gap 105 alsomakes it difficult to design thinner display units.

To address these problems, it has been proposed to fill the gap betweenthe liquid crystal display panel and the protective part with a resin(see, for example, Patent Document 1). However, the stress generatedwhen the resin cures and shrinks causes the deformation of the liquidcrystal display panel, resulting in disrupted orientation of the liquidcrystal material and other image defects. [Patent Document 1] JapanesePatent Application Laid-Open No. 2005-55641

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention has been devised in view of the above-describedproblems associated with prior art. Accordingly, it is an object of thepresent invention to provide a thin display unit that incorporates ahigh-luminance, high-contrast image display part that is free of imagedefects caused by the deformation of the display part.

Means for Solving the Problems

In an effort to achieve the foregoing object, the present inventors drewattention to the fact that the internal stress that builds up within aresin as the resin cures can be approximated by the product of thestorage modulus and the cure shrinkage of the cured resin, and found anideal resin composition for filling the above-described gap between thedisplay part and the protective part of a display unit, that is, a resincomposition that shrinks little when cured and has a storage modulus ina suitable range. This finding ultimately led to the present invention.

The present invention devised based on the above-described findingprovides an image display unit that includes an image display part, alight-transmitting protective part arranged on the image display part,and a cured resin layer arranged between the image display part and theprotective part. The cured resin layer has a transmittance of 90% orhigher in the visible range and a storage modulus at 25° C. of 1×10⁷ Paor less.

The present invention also provides the cured resin layer arrangedbetween the image display part and the light-transmitting protectivepart of the image display unit. As described above, the cured resinlayer has a transmittance of 90% or higher in the visible range and astorage modulus at 25° C. of 1×10⁷ Pa or less.

The present invention further provides a resin composition for formingthe above-described cured resin layer. The resin composition has a cureshrinkage of 5% or less and its cured resin has a transmittance of 90%or higher in the visible range when formed into a 100 μm-thick layer.The cured resin also has a storage modulus at 25° C. of 1×10⁷ Pa orless.

In the present invention, the image display part may be a liquid crystaldisplay panel.

In the present invention, the protective part may be formed of anacrylic resin.

In the present invention, the protective part may also be formed of anoptical glass.

EFFECT OF THE INVENTION

The resin composition of the present invention generates minimumshrinkage stress when it is applied between the image display part andthe protective part and cured, so that the effects of the stress on theimage display part and the protective part can be minimized. Thus, theimage display part and the protective part of the image display unit ofthe present invention are substantially free of distortion.

Since the cured product of the resin composition of the presentinvention, namely the cured resin, has a refractive index closer to thatof the panels used to make the image display part and the protectivepart, than does the gap between the liquid crystal display panel and theprotective part, light reflection is suppressed at the interface betweenthe protective part and the cured resin or at the interface between thecured resin and the image display part.

As a result, the image display unit of the present invention achieveshigh-luminance, high-contrast display of images without causing anyimage defects.

The image display unit of the present invention can effectively preventthe disrupted orientation of liquid crystal materials and other imagedefects and can therefore achieve high-quality display of imagesespecially when the image display part is a liquid crystal displaypanel.

Furthermore, the presence of the cured resin between the image displaypart and the protective part reinforces the image display unit of thepresent invention, making it resistant to high impacts.

In addition, the present invention can provide image display units thatare thinner than any of the conventional image display units that have agap between the image display part and the protective part.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing essential components of oneembodiment of display unit according to the present invention.

FIG. 2 is a cross-sectional view showing essential components of anotherembodiment of display unit according to the present invention.

FIG. 3 is a cross-sectional view showing essential components of stillanother embodiment of display unit according to the present invention.

FIG. 4 is a cross-sectional view showing essential components of aconventional display unit.

DESCRIPTION OF REFERENCE NUMERALS

-   1, 1B display unit-   2 display part-   3 protective part-   4 spacer-   5 cured resin or cured resin layer-   6, 7 polarizer

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be describedwith reference to the accompanying drawings, in which the same numeralsdenote the same or similar elements.

FIGS. 1 and 2 are cross-sectional views each showing one embodiment ofdisplay unit according to the present invention.

With reference to FIG. 1, a display unit 1 of the present embodimentincludes a display part 2 that is connected to a drive circuit (notshown) and displays predetermined images, and a light-transmittingprotective part 3 that is arranged in the vicinity of the display part 2and faces the display part 2.

In the display unit 1 of the present embodiment, the display part 2 is aliquid crystal display panel used in a liquid display apparatus.

The liquid crystal display apparatus is not limited to a particulartype, but can be applied to various systems. Examples of such liquidcrystal display apparatuses include those for use in cellular phones,portable game machines and other electronic devices.

When the display part 2 is a liquid-crystal display panel, polarizers 6,7 are arranged on each side of the display part 2 as shown in FIG. 2.

The protective part 3 is formed of a planar member having substantiallythe same size as the display part 2. The protective part 3 is preferablyformed of an optical glass or plastic (such as an acrylic resin).

The protective part 3 is spaced apart from the display part 2 by aspacer 4 arranged along the periphery of the display part 2. Thethickness of the spacer is about in the range of from 0.05 mm to 1.5 mmand serves to keep the distance between the surfaces of the display part2 and the protective part 3 at approximately 1 mm.

The display unit 1 includes a cured resin layer 5 provided between thedisplay part 2 and the protective part 3.

In the present invention, the cured resin layer 5 has a transmittance of90% or higher in the visible range and a storage modulus at 25° C. of1×10⁷ Pa or less, and preferably from 1.0×10³ to 1.0×10⁶ Pa. The resincomposition to make the cured resin layer 5 has a cure shrinkage of 5%or less, preferably 4.5% or less, and more preferably from 0 to 2%.

The image display unit of the present invention is preferably configuredwithout using the spacer 4 used in the above-described embodiments ofthe display unit 1 shown in FIGS. 1 and 2. Specifically, the resincomposition layer 5 and the protective part 3 are sequentially overlaidon the display part 2. Curing the resin composition completes an imagedisplay unit 1B as shown in FIG. 3 without providing the spacer. In thisconfiguration, the distance between the display part 2 and theprotective part 3 (thus, the thickness of the cured resins layer 5),which is determined by factors such as viscosity and density of theresin composition and weight of the protective part 3, is typically inthe range of from 50 μm to 200 μm. Such a configuration therefore makesit possible to design thinner image display units.

In the present invention, the resin composition to make the cured resinlayer 5 is preferably a photocurable resin composition in order toincrease the productivity, although other resins may also be used.

The resin composition for use in the present invention preferablycontains at least one polymer, such as polyurethane acrylates,polyisoprene acrylates and esters thereof, hydrogenated terpene resinsor butadiene polymers; at least one acrylate monomer, such as isobornylacrylate, dicyclopentenyloxyethyl methacrylate or 2-hydroxybutylmethacrylate; and at least one photopolymerization initiator, such as1-hydroxy-cyclohexyl-phenyl-ketone.

Since the protective part 3 often has a UV-cutting function to protectthe display part 2 against ultraviolet rays, the photopolymerizationinitiator for use in the present invention is preferably used togetherwith a photopolymerization initiator that can cure in the visible range(such as SpeedCure TPO (trade name), Nihon Siber Hegner KK).

The resin composition for use in the present invention is prepared suchthat the cured resin obtained by curing the resin composition by UVirradiation has a storage modulus (at 25° C.) of 1×10⁷ Pa or less, andpreferably in the range of from 1×10³ Pa to 1×10⁶ Pa, has a refractiveindex preferably in the range of from 1.45 to 1.55, and more preferablyin the range of from 1.51 to 1.52, and has a transmittance of 90% orhigher in the visible range when formed into a 100 μm thick layer.Different resin compositions containing the same major resin componentbut different auxiliary resin components and monomer components may becured to have different storage moduli (at 25° C.) that may, in somecases, exceed 1×10⁷ Pa. Those resin compositions that are cured to havea storage modulus (at 25° C.) of higher than 1×10⁷ Pa are not includedin the scope of the present invention.

The resin composition of the present invention also has a preferablecure shrinkage of 5% or less, more preferably of 4.5% or less, and stillmore preferably in the range of from 0 to 2%. In this manner, theinternal stress that builds up within the cured resin upon curing of theresin composition can be reduced, and the distortion generated at theinterface between the cured resin layer 5 and the display part 2 or theprotective part 3 can be prevented.

Thus, by arranging the resin composition between the display part 2 andthe protective part 3 and then curing the resin composition, the amountof light scattered at the interface between the cured resin layer 5 andthe display part 2 or the protective part 3 can be reduced. As a result,the luminance and the visibility of the displayed images can beimproved.

The magnitude of the internal stress that builds up within the curedresin upon curing of the resin composition can be evaluated by droppingthe resin composition onto a flat surface and measuring the averagesurface roughness of the cured resin. In practice, the distortiongenerated at the interface between the display part 2 or the protectivepart 3 and the cured resin arranged in between would be negligible if,for example, a cured resin obtained by dropping 2 mg of the resincomposition onto a glass plate and cured by UV irradiation to 90% or ahigher cure ratio has an average surface roughness of 6 nm or less. Byusing the resin composition of the present invention, this averagesurface roughness can be kept at 6 nm or less, and preferably in therange of 1 nm to 3 nm.

To fabricate the display unit 1 of the present invention, the spacer 4and a ridge (not shown) are arranged on the display part 2 along itsperiphery. A predetermined amount of the above-described photocurableresin composition is then poured over the display member 2 in the areainside the spacer and the ridge.

The protective part 3 is then placed on the display part 2 over thespacer 4 and the gap between the display part 2 and the protective part3 is completely filled with the resin composition.

Subsequently, the resin composition is irradiated with ultraviolet raysvia the protective part 3 to cure the resin composition. This completesthe desired display unit 1.

When it is desired to fabricate the display unit 1B in which the spacer4 is omitted, the above-described photocurable resin composition isfirst applied onto the display part 2. The protective part 3 is thenplaced over the coating of the resin composition and the ultravioletrays are irradiated onto the resin composition from the side of theprotective part 3.

In the image display units 1, 1B of the present invention obtained inthe foregoing manner, the effects of the stress generated as the resincures and shrinks on the display part 2 and the protective part 3 can beminimized, so that little or no distortion is generated in the displaypart 2 and the protective part 3. Since the display part 2 is notdeformed during the production, it can display images at high luminanceand high contrast without causing any image defects.

In addition, the cured resin 5 that fills the gap between the displaypart 2 and the protective part 3 in the present embodiment reinforcesthe display unit 1 so that it can withstand high impacts. This makes itpossible to design thinner display units 1.

In particular, when the image display part 2 is a liquid crystal displaypanel, the present invention can provide a liquid crystal displayapparatus that can effectively prevent disrupted orientation of liquidcrystal materials and other image defects and can thus achievehigh-quality display of images especially.

While the present invention is suitable for use in the above-describedliquid crystal display apparatuses, the invention is also applicable tovarious other panel displays, such as organic EL apparatuses and plasmadisplay apparatuses.

EXAMPLES

The present invention will now be described in detail with reference toExamples and Comparative Examples, which are not intended to limit thescope of the invention in any way.

Example 1

The following components were kneaded together in a kneader to make aresin composition of Example 1: 50 parts by weight of polyurethaneacrylate, 30 parts by weight of isobornyl acrylate, 3 parts by weight ofa photopolymerization initiator and 1 part by weight of aphotopolymerization initiator for visible-range.

Example 2

The following components were kneaded together in a kneader to make aresin composition of Example 2: 70 parts by weight of an ester formedfrom a maleic anhydride adduct of a polyisoprene polymer and2-hydroxyethyl methacrylate, 30 parts by weight ofdicyclopentenyloxyethyl methacrylate, 10 parts by weight of2-hydroxybutyl methacrylate, 30 parts by weight of a hydrogenatedterpene resin, 140 parts by weight of a butadiene polymer, 4 parts byweight of a photopolymerization initiator and 0.5 parts by weight of avisible-range photopolymerization initiator.

Example 3

The following components were kneaded together in a kneader to make aresin composition of Example 3: 100 parts by weight of an ester formedfrom a maleic anhydride adduct of a polyisoprene polymer and2-hydroxyethyl methacrylate, 30 parts by weight ofdicyclopentenyloxyethyl methacrylate, 10 parts by weight of2-hydroxybutyl methacrylate, 30 parts by weight of a hydrogenatedterpene resin, 210 parts by weight of a butadiene polymer, 7 parts byweight of a photopolymerization initiator and 1.5 parts by weight of avisible-range photopolymerization initiator.

Comparative Example 1

The following components were kneaded together in a kneader to make aresin composition of Comparative Example 1: 50 parts by weight ofpolybutadiene acrylate, 20 parts by weight of hydroxyethyl methacrylate,3 parts by weight of a photopolymerization initiator and 1 part byweight of a visible-range photopolymerization initiator.

Comparative Example 2

The following components were kneaded together in a kneader to make aresin composition of Comparative Example 2: 50 parts by weight ofpolyurethane acrylate, 30 parts by weight of tricyclodecane dimethanolacrylate, 3 parts by weight of a photopolymerization initiator and 1part by weight of a visible-range photopolymerization initiator.

Comparative Example 3

The following components were kneaded together in a kneader to make aresin composition of Comparative Example 3: 50 parts by weight ofpolybutadiene acrylate, 20 parts by weight of isobornyl acrylate, 3parts by weight of a photopolymerization initiator and 1 part by weightof a visible-range photopolymerization initiator.

Evaluation 1

Each of the resin compositions prepared in Examples 1 through 3 andComparative Examples 1 through 3 was poured onto a 100 μm-thick whiteglass plate to a predetermined thickness. The plates were transported ona UV-conveyor to obtain cured resins having a predetermined thickness.The cured resins were used as samples.

The light transmittance, elastic modulus, cure shrinkage and surfaceroughness of each sample were determined as described below.

[Light Transmittance]

Using a UV-Visible spectrophotometer (V-560, Jasco Corp.), each sample(with 100 μm-thick cured resin) was analyzed for the transmittance inthe visible range. It turned out that all of the samples had 90% or ahigher transmittance.

[Elastic Modulus]

Using a viscoelastometer (DMS6100, Seiko Instruments Inc.), the elasticmodulus (at 25° C.) of each sample (with 2 mm-thick cured resin) wasmeasured at a frequency of 1 Hz.

[Cure Shrinkage]

The cure shrinkage of each sample was determined by the followingequation using the difference in the specific gravity between theuncured resin solution and the cured solid product, as measured by anelectronic specific gravity meter (SD-120L, Mirage Co.).

cure shrinkage(%)={(specific gravity of cured resin−specific gravity ofresin solution)/(specific gravity of cured resin)}×100

[Surface Roughness]

Using a three-dimensional non-contact surface roughness meter (ZygoCorp.), each sample (with 1 mm-thick cured resin) was analyzed for thedistortion (Ra: average surface roughness) in a predetermined area (2.93mm×2.20 mm) of the glass plate surface caused by the internal stressgenerated during UV curing.

These results are shown in Table 1.

TABLE 1 Properties of Examples and Comparative Examples andcorresponding evaluation results Elastic modulus Cure shrinkage Ra:average surface (Pa) (%) roughness (nm) Example 1 1 × 10⁶ 4.5 5.5Example 2 1 × 10⁴ 1.8 2.7 Example 3 4 × 10³ 1.0 1.5 Comparative 2 × 10⁷5.6 12.4 Example 1 Comparative 3 × 10⁸ 4.3 36.5 Example 2 Comparative 5× 10⁸ 5.6 64.2 Example 3

As can be seen from Table 1, the average surface roughness Ra was from1.5 nm to 5.5 nm in each of Examples 1 through 3, indicating thatsamples in these Examples were each distorted little.

In comparison, Ra was significantly large in each of Comparative Example1 (Ra=12.4 nm), Comparative Example 2 (Ra=36.5 nm) and ComparativeExample 3 (Ra=64.2 nm), suggesting that the internal stress generatedupon curing of the resin in each of Comparative Examples 1 through 3caused distortion at the interface between the resin and the glassplate.

Evaluation 2 [Impact Resistance]

The resin composition of Example 1 was cured between a 50 mm×50 mm×0.5mm glass plate (display part) and a 50 mm×50 mm×0.5 mm polycarbonateplate (protective part) to form a 0.1 mm-thick layer between the twoplates. The resulting panel served as the sample panel of Example. Inthis configuration, the spacer was omitted and the sample panel had atotal thickness of 1.1 mm. To fabricate the sample panel, the resincomposition of Example 1 was first applied to the glass plate and thepolycarbonate plate was placed over the coating of the resincomposition. The resin composition was then cured by the irradiation ofUV from the side of the polycarbonate plate.

Meanwhile, a sample panel having the conventional configuration as shownin FIG. 4 was prepared. The liquid crystal display panel (display part)102 and the protective part 103 used were identical to those used tomake the sample panel of Example. The display part and the protectivepart were assembled with 1.0 mm thick spacers arranged in between tomake the sample panel of Comparative Example having a 1.0 mm air gap anda total thickness of 2.0 mm.

Each of the sample panels of Example and Comparative Example was securedto a mount by the periphery using a predetermined jig. A panel breakagetest was then performed by perpendicularly pressing a press member, 5 mmin diameter, against the surface of the protective part at a press speedof 1 mm/sec.

The sample panel of Comparative Example with the air gap formed betweenthe display part and the protective part broke at 1 N/cm², whereas thesample panel of the present invention broke at 1.43 N/cm².

The results demonstrate that the panel of Example has a press strengththat is 43% higher than that of the panel of Comparative Example, yethas a decreased thickness as compared to the panel of ComparativeExample.

1. An image display unit comprising: an image display part; a light-transmitting protective part arranged on the image display part; and a cured resin layer arranged between the image display part and the protective part, wherein the cured resin layer has a transmittance of 90% or higher in the visible range and a storage modulus at 25° C. of 1×10⁷ Pa or less.
 2. The image display unit according to claim 1, wherein the storage modulus of the cured resin layer is in a range of from 1×10³ Pa to 1×10⁶ Pa.
 3. The image display unit according to claim 1, wherein the cured resin layer has a thickness of from 50 μm to 200 μm.
 4. The image display unit according to claim 1, wherein the image display part is a liquid crystal display panel.
 5. The image display unit according to claim 1, wherein the protective part is formed of an acrylic resin.
 6. The image display unit according to claim 1, wherein the protective part is formed of an optical glass.
 7. A resin composition for forming a cured resin layer arranged between an image display part of an image display unit and a light-transmitting protective part, the resin composition having a cure shrinkage of 5% or less, wherein a cured resin obtained by curing the resin composition has a transmittance of 90% or higher in the visible range when formed to have a thickness of 100 μm, and has a storage modulus at 25° C. of 1×10⁷ Pa or less.
 8. The resin composition according to claim 7, containing at least one polymer selected from the group consisting of a polyurethane acrylate, a polyisoprene acrylate and an ester thereof, a hydrogenated terpene resin and a butadiene polymer; at least one acrylate monomer selected from the group consisting of isobornyl acrylate, dicyclopentenyloxyethyl methacrylate and 2-hydroxybutyl methacrylate; and a photopolymerization initiator.
 9. The resin composition according to claim 7, wherein a cured resin obtained by dropping 2 mg of the resin composition onto a glass plate and cured by UV irradiation has an average surface roughness of 6 nm or less.
 10. A cured resin layer arranged between an image display part of an image display unit and a light-transmitting protective part, the cured resin layer having a transmittance of 90% or higher in the visible range and a storage modulus at 25° C. of 1×10⁷ Pa or less. 